The invention relates to a device having a first and a second ferromagnetic layer separated by a non-magnetic spacer layer, wherein the resistance is dependent on the orientation of the magnetisation directions of the first and second ferromagnetic layers.
The Giant Magneto-Resistance (GMR) effect and the Tunnel Magneto-Resistance (TMR) effect provide possibilities to realise readout heads for magnetic recording, sensitive magnetic sensors and nonvolatile magnetic memories (MRAM's). Such devices comprise a first and a second ferromagnetic layer separated by a non-magnetic spacer layer. The magnetization of one of the layers is fixed (fixed layer), the other (free layer) can have any orientation with respect to the magnetisation of the fixed layer (for sensors) and for magnetic memories can be switched between two directions (i.e. parallel or anti-parallel to the fixed magnetisation). Due to the GMR (TMR) effect the resistance for both configurations is different, and the state of the memory (`1` or `0`) can be determined by measuring the resistance of the GMR system. Switching the magnetisation direction of the free layer changes the state of the MRAM. Conventionally an additional conductor is used to switch the magnetisation direction of the free layer. Conventional MRAMs require a relatively large write current. Because of power consumption restrictions this current should be as small as possible. However, on the other hand the memory should be insensitive to disturbing external magnetic fields (to avoid unintended erasing of data). Similar techniques are used in read-out heads for magnetic recording in which the resistance is dependent on the magnetisation direction in the free layer vis-a-vis the fixed layer. In such read-out heads it is advantageous if the magnetisation direction in the fixed layer can be reset relatively easily.